Recording method for a phase-change optical recording medium

ABSTRACT

The present invention provides a recording method for a phase-change optical recording medium. The recording method of the present invention contains the step of irradiating an electromagnetic wave having a multipulse pattern so as to perform recording on a phase-change optical recording medium containing a phase-change recording layer. This method is characterised in that a starting time of a front pulse of the multipulse pattern delays 0.5T to 1.25T from a starting point of the first reference clock relative to the recording mark, where T is a reference clock of the multipulse pattern.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a recording method of aphase-change optical disk, namely, a rewritable optical disk. Thismethod is suitably applied for a high volume optical medium, DVD+RW, orthe like.

[0003] 2. Description of the Related Art

[0004] Phase-change recording media, which are used for CD and DVDrewritable recording media have rapidly become very popular due to theirhigh capacity, high-speed recording, and high compatibility with ROM(Read Only Memory). In recent years, it is required thatrecording/reproducing of mass image data is carried out at high speed,and higher speeds are being demanded of phase-change recording media.However, it is desirable that a high linear velocity recording diskwhich can be recorded at a high linear velocity, should be able to berecorded also in a low-speed drive for low linear velocity recordingdisks which record at a low linear velocity. This is possible with CD-R,which can record over a wide range of linear velocity.

[0005] However, in the case of the above-mentioned phase-changerecording medium, it is difficult to perform recording over a wide rangeof linear velocity. In order to perform recording at a high linearvelocity, a high power laser which outputs a high recording power isrequired. The recording power of the laser light used in a low-speeddrive is usually lower than the recording power of the laser lightoutput in a high-speed drive for high linear velocity recording. Hence,it is difficult to record a high linear velocity recording disk in alow-speed drive.

[0006] The aforesaid phase-change recording medium is usually optimizedfor recording at a high linear velocity. In the case of a phase-changerecording medium designed in this way, the recording power to record ishigher than the optimal recording power for a low recording linearvelocity. Thus, in order to perform recording at a lower recording powerwith this phase-change optical recording medium, the sensitivity of thisphase-change optical recording medium must be increased. In order toincrease sensitivity of this phase-change optical recording medium, thereflectance of this phase-change optical recording medium can belowered. However, when designing this phase-change optical recordingmedium as a DVD, it is necessary to maintain compatibility with DVD-ROM.Thus, the above-mentioned reflectance cannot be made lower as desired.

[0007] The highest recording linear velocity in rewritable DVD currentlycommercialized in the past several years is 2.4×. A phase-change opticalrecording medium, which can be recorded at a higher recording linearvelocity than 2.4× and also in a low-speed drive, namely, which isdownward compatible, has not yet been provided.

[0008] In order to provide downward compatibility, it is required toselect the composition of the above-mentioned phase-change opticalrecording medium and the material of the recording layer, and optimizethe recording conditions of this phase-change optical recording medium,so that it is recordable at a low recording power and the recordingpower margin is large.

[0009] In the prior art, for example in Japanese Patent (JP-B) No.3124720 or Japanese Patent Application Laid-Open (JP-A) No. 2000-322740,by controlling the pulse-width of a laser pulse-like waveform, it can bemade CAV (Constant Angular Velocity) recording possible at 2.4×. In thecase of rewritable DVD, however, there is a problem that it is difficultto realize a recording linear velocity higher than 2.4× together withdownward compatibility so that recording can also be performed in alow-speed drive.

[0010] In JP-B No. 2844996, for example, instead of using a fixederasing power for high speed recording, a method of modulating theerasing power by the reproduction power range is disclosed. However, inthe case of this method, a sufficient erasure cannot be performed, andthere is the problem that an amorphous phase may be formed depending onthe level of the erasing power.

[0011] Also, for example, in JP-B No. No. 2941703, a method wherein arear edge cooling pulse interval is basically eliminated when forming arecord mark, is described. However, in the case of this method, there isa problem that it is difficult to form a record mark of predeterminedlength.

[0012] In the case of DVD, such phase-change optical recording mediumand recording method thereof are required that recording can beperformed at a recording linear velocity as fast as 4× (as 1× linearvelocity is 3.49 m/s, this is approx. 14 m/s (13.96 m/s)), and also witha recording power below the optimal recording power of a phase-changerecording medium for recording of a recording linear velocity of 1× to2.4×.

[0013] In this regard, it is important to optimize the crystallizationrate of the recording layer in the phase-change optical recordingmedium. In the recording layer, the overwrite characteristics,particular the characteristics of the first overwrite, deteriorate whenrecording is performed at a high linear velocity. Hence, to enablerecording at a high linear velocity, it is important to optimize theelements and elemental composition of this recording layer so that thecrystallization rate in this recording layer increases.

[0014] In order to form a record mark (amorphous phase) in the aforesaidrecording layer in the case of the aforesaid phase-change opticalrecording medium, it is necessary to heat the material of this recordinglayer to near the melting point thereof and to perform quenching in ashort time. The crystallization rate in the recording layer is larger,the larger is the temperature gradient over time, and the longer is thenon-heating time (cooling time) required to suppress recrystallizationis longer. However there is a limit to the heating time and coolingtime. During recording at a high linear velocity where it is difficultto raise the temperature in a short time, therefore, the recording powermust be increased. Also when recording at a low linear velocity, theaforesaid crystallization rate in the aforesaid recording layer islarge, so the recording power must likewise be increased.

[0015] Accordingly, in a phase-change optical recording medium forrecording at a high linear velocity, the aforesaid crystallization ratecannot be made too high. Consequently, if a fixed erasing power isirradiated, an amorphous phase is easily formed even if the erasingpower is not so high, and the erasing power cannot be increased toomuch, the higher is the linear velocity. For this reason, theabove-mentioned crystallization rate may be optimized at an intermediatelinear velocity between a low linear velocity and a high linearvelocity. However, in this case, the erasing power is not sufficient fora high linear velocity, and mark erasure properties during overwrite arepoor.

SUMMARY OF THE INVENTION

[0016] It is therefore an object of the present invention, whichresolves the problems inherent in the prior art, to provide a recordingmethod suitable for a phase-change optical recording medium which canrecord at a high linear velocity, and which when recording at a lowlinear velocity, can record at almost the same recording power as aphase-change optical recording medium suitable for a low linearvelocity. It further aims to provide a recording method which providesgood overwrite characteristics in CAV recording or CLV (Constant LinearVelocity) recording.

[0017] The first aspect of the recording method for a phase-changeoptical recording medium of the present invention comprises the step ofirradiating an electromagnetic wave having a multipulse pattern so as toperform recording, erasing and overwriting on a phase-change opticalrecording medium containing a phase-change recording layer, in which themultipulse pattern contains pulses of a peak power (Pp), an erasingpower (Pe) and a bias power (Pb), where the pulses of the peak powercontain a front heating pulse (OP1), an intermediate heating pulse (OPj)and a rear heating pulse (OPm), and the pulses of the bias power containa front cooling pulse (FP1), an intermediate cooling pulse (FPj) and arear cooling pulse (FPm). Here, a starting time of a front pulse delays0.5 T to 1.25 T (T: a reference clock of the multipulse pattern) from astarting point of the first reference clock relative to the recordingmark. In this recording method, several aspects are preferred: (1) anending time of a rear pulse is T−OPm or less, earlier than an endingpoint of the last reference clock relative to the recording mark; (2)the starting time of the front pulse delays more than 1 T, and 1.25 T orless, from the starting point of the first reference clock, with amaximum recording linear velocity among recordable recording linearvelocities to the phase-change optical recording medium; (3) the endingtime of the rear pulse is T−OPm earlier than an ending point of the lastreference clock, with the maximum recording linear velocity; (4)recording is performed at a recording linear velocity within a range ofan intermediate recording linear velocity to the maximum recordinglinear velocity with respect to the recordable recording linear velocityto the phase-change optical recording medium.

[0018] In the second aspect of the recording method of the presentinvention, when a recording linear velocity is continuously changes withrespect to an inner circumference to an outer circumference of thephase-change optical recording medium, pulse widths of the front heatingpulse (OPl), the intermediate heating pulse (OPj), and the rear heatingpulse (OPm) are controlled by adjusting a sum of a time which isproportional to the reference clock relative to a recording linearvelocity within a range of the minimum recording linear velocity and theintermediate recording linear velocity and a time being independent fromthe reference clock, or, a time which is proportional to the referenceclock relative to a recording linear velocity within a range ofone-third of the maximum linear velocity to the maximum linear velocity.In this recording method, if the aforesaid pulse widths are controlledby adjusting the sum of the time which is proportional to the referenceclock relative to a recording linear velocity within a range of theminimum recording linear velocity and the intermediate recording linearvelocity and the time being independent from the reference clock, themethod is preferably applied with a recording linear velocity within therange of the minimum recording linear velocity to the intermediaterecording linear velocity, and a recording linear velocity within therange of the one-third of the maximum recording linear velocity to themaximum recording linear velocity.

[0019] In the third aspect of the optimal recording method of thepresent invention, in a case of recording only with the maximumrecording linear velocity regardless to a recording position on thephase-change optical recording medium, the aforesaid pulse widths arecontrolled by adjusting a sum of the time which is proportional to thereference clock and the time being independent from the reference clock.Here, the time independent from the reference clock is 0.5 nano secondsor more.

[0020] In the fourth aspect of the recording method of the presentinvention, the multipulse pattern further contains at least onecompensation pulse which includes a pulse of the erasing power Pe and apulse of a second erasing power Pe2 after the rear cooling pulse. Here,the second erasing power Pe2 is higher than the erasing power Pe. Inthis aspect of the recording method, a few aspects are preferred: (1)the compensation pulse is contained in the multipulse pattern when atleast the shortest record mark is recorded among recordable record markswith the phase-change optical recording medium and the recording linearvelocity; and (2) at least the maximum recording linear velocity isapplied so as to perform recording.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a cross-sectional view showing an example of the laminarstructure of the phase-change optical recording medium used by thepresent invention.

[0022]FIG. 2 is a diagram showing an example of a light emissionwaveform used to perform recording and erasure of the prior art.

[0023]FIG. 3 is a diagram showing an example of a light emissionwaveform used to perform recording and erasure according to the presentinvention.

[0024]FIG. 4 is a graph showing the dTtop dependency of jitter after oneoverwrite at a linear velocity of 14 m/s.

[0025]FIG. 5 is a graph showing the relation between jitter and dTera.

[0026]FIG. 6 is a graph showing the relation between jitter and powermargin.

[0027]FIG. 7 is another graph showing the relation between jitter andpower margin.

[0028]FIG. 8 is a graph showing the dTtop dependencies of jitter withrespect to each linear velocity at the first overwriting.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] As shown in FIG. 1, the phase-change optical recording mediumused by the present invention is formed by laminating a transparentsubstrate 1, lower dielectric protective layer 2, phase-change recordinglayer 3 which undergoes a reversible phase-change between an amorphousphase and a crystalline phase, an interface layer 7, upper dielectricprotective layer 4, anti-sulfuration layer 5 and reflective layer 6, inthat order. The interface layer 7 is not indispensable.

[0030] For the aforesaid transparent substrate 1, plastic or glass, suchas transparent polycarbonate (PC), polymethacrylic acid (PMMA) or thelike, which is transparent to the wavelength of therecording/reproducing light, may be used.

[0031] There is no particular limitation on the material of the lowerdielectric protective layer 2 disposed between the transparent substrate1 and the phase-change recording layer 3, and the material of the upperdielectric protective layer 4 disposed between the phase-changerecording layer 3 and the reflective layer 6. Although they may beselected according to the purpose, examples are metal oxides such asSiO_(x), ZnO, SnO₂, Al₂O₃, TiO₂, In₂O₃, MgO, ZrO₂, Ta₂O₅, or the like;nitrides such as Si₃N₄, AlN, TiN, BN, ZrN, or the like; sulfides such asZnS, TaS₄, or the like; and carbides such as SiC, TaC, B₄C, WC, TiC, Zror the like.

[0032] These materials can also be used alone or in admixture. Of these,a mixture of ZnS and SiO₂ is generally used as the phase-changerecording medium. As the mixing ratio thereof, 80:20 (molar ratio) issatisfactory. The aforesaid lower dielectric protective layer 2preferably has a low thermal conductivity, and its specific heat issmall. It is preferred that crystallization is not caused byoverwriting, cracking is not occurred by repeated heating/quenchingcycles, and there is no elemental diffusion. ZnS-SiO₂ (80:20) satisfiesthese conditions, and is used also for the upper dielectric protectivelayer 4. In mixtures wherein ZrO₂ contains 3 mol % to 6 mol % of Y₂O₃,the refractive index is almost the same as or is larger than that ofZnS-SiO₂, and its thermal conductivity is also low.

[0033] When the bulk thermal conductivity was measured by the laserflash process, in a type of the bulk containing ZrO₂ as the mainingredient, ZrO₂.Y₂O₃ (3 mol %), ZrO₂.SiO₂ (5 mol %).Y₂O₃ (3 mol %),ZrO₂.TiO₂ (50 mol %).Y₂O₃ (3 mol %), and ZrO₂.TiO₂ (40 mol %).SiO₂ (20at %).Y₂O₃ (3 mol %) were respectively 5.1, 3.5, 1.73, 2.6 (W/m·K), andZnS.SiO₂ (20 mol %) was 8.4 (W/m·K).

[0034] The refractive index (n) was 2 or more in all cases except forZrO₂.SiO₂ (5 mol %). MgO may be used instead of Y₂O₃. All thesematerials are generally used for preventing cracking of the target whena target is manufactured for film-forming by a sputtering method.

[0035] For references, phase-change optical recording mediums wereformed using these materials for the upper dielectric protective layer4, and the storage properties of record mark thereon were examined at80° C. and 85% RH after recording. If the content of ZrO₂ is 50 at % ormore, the mark disappeared or jitter deterioration was large. However,the repeat overwrite characteristics of ZrO₂ containing materials aregood, and there was less jitter degradation after recording 1,000 timesthan with ZnS.SiO₂. There is more effect in overwriting at a high linearvelocity.

[0036] However, as the aforesaid dielectric protective layer 4, ZnS-SiO₂(80:20) is more suitable.

[0037] In this regard, in order to harness the effect which improvesthis overwrite characteristic, the effect of providing a ZrO₂ materialas an interface layer disposed between the phase-change recording layerand the upper dielectric protective layer was examined.

[0038] As a result, it was found that when the thickness was within arange of 1 nm to 5 nm, this effect was maintained and deterioration ofstorage reliability was considerably suppressed.

[0039] The interface layer has the following effect. This layer is in acrystalline state and the lattice constants thereof is close to that ofthe aforesaid phase-change recording layer so that this interface layerencourages crystal growth of the phase-change recording layer. Althoughthe interface layer is not in a crystallized state, it assists crystalgrowth so as to increase the erasure ratio and improve overwritecharacteristics.

[0040] Moreover, as wettability is poor, when the recording layer is ina molten state, fluidity is suppressed and local volume change of thisrecording layer is suppressed, overwrite characteristics also improve.

[0041] The thickness of the lower dielectric protective layer is withina range of about 40 nm to about 250 nm, and preferably within a range of45 nm to 80 mm. If the thickness is less than about 40 nm,environment-proof protective functions are reduced, the heat dissipationeffect is lowered so that deterioration of repeat overwritecharacteristics increases. If the thickness is more than about 250 nm,in the film-forming process by sputtering or the like, film peeling orcracking occurs due to the rise of film temperature.

[0042] Moreover, the thickness of the transparent substrate is less than0.6 mm. If the thickness of the transparent substrate reaches 0.6 mm,deformation of the transparent substrate may increase, and aftersticking, it may be impossible to correct the deformation.

[0043] The thickness of the upper dielectric protective layer is in arange of about 5 nm to about 50 nm, and preferably in a range of 8 nm to20 nm. If the thickness is less than about 5 nm, recording sensitivitywill fall, whereas if the thickness is more than about 50 nm,deformation occurs due to temperature rise, and repeat overwritecharacteristics will worsen due to lower heat dissipation properties.

[0044] The aforesaid reflective layer may comprise a metallic material,such as Al, Ag, Cu, Pd, Cr, Ta, Ti and the like. The thickness thereofis preferably within a range of 50 nm to 250 nm. If the reflective layeris excessively thick, heat dissipation properties are more improved, butdue to temperature rise of the medium while producing the thin film,deformation of the substrate does occur. If the reflective layer isexcessively thin, heat dissipation properties will worsen and recordingproperties will deteriorate.

[0045] The characteristics of the above-mentioned reflective layer areimproved by using Ag which has a higher thermal conductivity. For thisreason, Ag or Ag alloy is suitably used.

[0046] When the linear velocity increases, the cooling rate will becomelarge. Accordingly, an amorphous mark is easily formed, but as therecording layer is heated to near its melting point when the mark isformed, the heating pulse time of the light emission pulse had to belengthened. On the other hand, if the heating time is lengthened, thecooling time is shortened so the cooling time may not be sufficient andit will become difficult to form a mark. This is because the sum of thepulse times of one heating and cooling is a reference clock, and changesare made within these limitations.

[0047] Thus, in order to improve the cooling efficiency of the medium,Ag may be suitably used. However, when the upper dielectric protectivelayer contains S (sulfur) and the reflective layer is Ag, Ag₂S is easilyformed under high temperature and high humidity. This leads tocharacteristic degradation and generates defects, which poses a problem.

[0048] It is then necessary to provide an anti-sulfuration reactionlayer between the reflective layer and the upper dielectric protectivelayer. As a result of intensive studies on oxides, nitrides, carbidesand metals performed so far, preferable materials for theanti-sulfuration reaction layer are Si and SiC, and ZrO₂, MgO andTiO_(x) are also suitable. SiC prevents the reaction of Ag and S, andthe effect thereof is large even with the thickness of as thin as 3 nm.The thickness of the anti-sulfuration reaction layer is within a rangeof about 2 nm to about 10 nm. If the thickness is more than 10 nm, itwill separate from the reflective layer, so the heat dissipationefficiency falls and as the absorption constant is high, and thereflectance tends to fall.

[0049] By using Ag alone for the reflective layer, properties improve.In view of the corrosivity of Ag itself and adhesion to theanti-sulfuration layer when Ag is used alone, by optimizing sputteringconditions (argon gas pressure) during thin film production, the crystalparticle size of Ag is reduced, and by suppressing particle growth, thethin film surface of Ag becomes flat and smooth. When the particle sizeis large, peeling easily occurs from where the adhesion is weak.

[0050] Further, to improve adhesion, Ag can still be used alone byoptimizing the curing conditions and thickness of the ultraviolet-curingacrylic resin which is used as an environmental protection layer on thereflective layer. If Ag is used alone, however, there is a concern thatdeterioration may occur due to manufacture under less than optimumconditions, to storage conditions of the substrate before stickingwithout a recording film, to moisture absorption of the substrate itselfand moisture absorption of the ultraviolet curing resin.

[0051] In this regard, reliability is improved by using an alloycontaining 95 at % or more Ag. If the addition amount of other metallicelement to Ag exceeds 5 at %, thermal conductivity considerablydecreases. For this reason, the addition amount is preferably 2 at % orless.

[0052] As additional elements, Cu and Ni are preferably since theysuppress particle size growth without much lowering thermal conductivityand improve environmental resistance. When producing an Ag film bysputtering, to reduce the crystal particle size of the Ag film, thepower applied between the substrate and the target may be 3 W or less.

[0053] The aforesaid phase-change recording layer has conventionallybeen based on a eutectic composition in the vicinity of Sb70Te30.AgInSbTe and AgInSbTeGe materials which contains Ag, In and Ge aresuitable for high-density recording at high linear velocity, and havetherefore conventionally been used. The higher is the ratio of Sb to Teor if the amount of Sb is more than 80 at %, the crystallization rateincreases, but storage properties are exceedingly poor and it becomesdifficult to form an amorphous phase. Therefore, a desirable amount ofSb for high linear velocity recording is within a range of 65 at % to 80at %.

[0054] On the other hand, the amount of Te is preferably within a rangeof 15 at % to 25 at %. Although Ge does not increase the crystallizationrate, Ge improves storage properties of the record mark under the hightemperature environment and is an essential element. The binding energyof Ge and Te is large. Moreover, the larger is the Ge addition amount,the higher is the crystallization temperature which means better storageproperties. However, if Ge is excessively added, the crystallizationtemperature further increases and the crystallization rate slows down,so 5 at % is preferred. Although Ag stabilizes record marks, thecrystallization temperature can not sufficiently increase thecrystallization temperature. If Ag is excessively added, thecrystallization rate drops, so a large amount thereof cannot be used. Onthe other hand, it also has the effect of stabilizing the crystallinestate, so the amount of Ag in the phase-change recording layer ispreferably 3 at % or less.

[0055] In increases crystallization rate and increases crystallizationtemperature, so storage properties are improved. If a large amount isadded, however, the material tends to segregate. Deterioration of repeatoverwrite characteristics and deterioration with respect to reproductionoptical power occur, so the amount of In in the phase-change recordinglayer is preferably 5 at % or less. In addition to In, Ga also increasesthe crystallization rate. Ga accelerates the crystallization rate morethan an identical amount of In, but it also increases thecrystallization temperature. If the amount of Ge is 5 at % and Ga is 5at % or more, the crystallization temperature will greatly exceed 200°C. and may rise to 250° C. or more. As a result, in the initializationprocess for crystallizing the recording layer from the amorphous state,the reflectance distribution around the track increases, and leads torecording characteristic and data errors. For this reason, when Ga isused as a supplementary element to accelerate the crystallization rate,the amount of Ga in the phase-change recording layer is preferably 3 at% addition or less.

[0056] There is a limit to the use of AgInSbTeGe as a higher linearspeed material. As a result of studying elements which replace Ag andIn, it was found that although Mn accelerates the crystallization rate,it is effective as it does not increase the temperature rise more thannecessary. Mn increases crystallization rate, like In. Even if a largeamount thereof is used, storage properties are satisfactory withoutdeteriorating overwrite characteristics. Although crystallizationtemperature also increases, the increase amount in the crystallizationtemperature relative to the amount of Mn is small, and reproductivephotodegradation is also small. In the present invention, it issufficient if 5 at % of Mn is added.

[0057] Thus, a GeMnSbTe material is also a suitable material for highlinear velocity. Further, a GeMnSbTe material wherein Ga is added toimprove crystallization rate and storage properties is also effective.The thickness of the recording layer, is preferably within a range of 10nm to 20 nm. If the thickness thereof is less than 10 nm, thereflectance difference between the crystal phase and amorphous phase issmall. If the thickness thereof is more than 20 nm, recordingsensitivity and repeat overwrite characteristics will worsen.

[0058] As a material for the phase-change recording layer, apart fromthe aforesaid materials, Ag.In.Sb.Te, Ge.Ga.Sb.Te, Ge.Sb.Te,Ge.Sn.Sb.Te, Ge.Sn.Sb, Ge.In.Sb.Te, Ga.Sn.Sb, Ge.Ag.Sn.Sb, Ga.Mn.Sb,Ga.Sn.Sb.Se, and the like can also be used.

[0059] Recording/reproducing for the above phase-change recording mediumcan be performed with the recording wavelength of 400 nm to 780 nm.

[0060] In the case of DVD, a recording wavelength of 650 nm to 660 nm isused. The numerical aperture of the object lens is then set to 0.60 to0.65, and the beam diameter of the incident light is set to 1 μm orless. Hence, the thickness of the substrate is set to 0.6 mm, and theaberration is made small.

[0061] The pitch between the grooves in which the mark is written is0.74 μm, the depth of the grooves is 15 nm to 45 nm and the groove widthis 0.2 μm to 0.3 μm.

[0062] The groove has a wobble having a frequency of approximately 820kHz. The address part is encoded in the wobble by modulating the phaseof the frequency. This phase-change is detected and decoded to a binarysignal, and an address (number) is read.

[0063] The amplitude of this wobble is 5 nm to 20 nm. The recordinglinear density is 0.267 μm/bit, and recording is performed using the(8-16) modulation method. In this case, the shortest mark length will be0.4 μm. 2× of DVD is recorded at a linear velocity of 7 m/s (6.98 m/s)and with the reference clock whose frequency is set to 52.3 MHz (T:19.1nanoseconds, T is a reference clock). 4× of DVD is recorded at a linearvelocity of 14 m/s (13.96 m/s), and with the reference clock whosefrequency is set to 104.6 MHz (T:9.56 nanoseconds). The linear velocityis changed from 1× to 4× while irradiating an erasing power of fixedmagnitude continuously or at regular intervals to the phase-changeoptical recording medium. If the reflective signal strength at this timeis measured, the reflective intensity begins to decrease from a certainlinear velocity, and at a higher linear velocity, the reflectiveintensity further decreases, and eventually becomes saturated.

[0064] When a substrate surface of the phase-change optical recordingmedium is measured using a pickup of wavelength 659 nm and NA 0.65, anda 12 mW erasing power is irradiated, the linear velocity at whichreflectance begins to fall is from 9 m/s to 10.5 m/s.

[0065] Conventionally, a phase-change optical recording medium optimizedat 4× requires a higher recording power than a recording power requiredfor a medium optimized at a lower linear velocity. In order to makerecording possible by the same recording power as a phase-change opticalrecording medium corresponding to from 1× to 2.4×, the linear velocityat which the reflectance begins to fall is preferably earlier than 2.4×,i.e., 8.4 m/s, and more preferably 0.5 m/s to 1 m/s.

[0066]FIG. 2 is a light emission waveform used conventionally to performrecording/erasing. As irradiation powers, there are peak power (Pp),erasing power (Pe) and bias power (Pb). As a pulse pattern, there are afront heating pulse OP1, an intermediate heating pulse OPj (j=2 to m−1),and a rear heating pulse OPm, at which the peak power (recording power)is applied, for heating the recording layer. In addition, there arecooling pulses of a front cooling pulse FP1 and an intermediate coolingpulse FPj. Here, the sum of the time of the intermediate heating pulseOPj and the intermediate cooling pulse FPj, is T.

[0067] The number of pulses is (n−1) or (n−2) relative to the recordmark length nT. Up to a linear velocity of 2.4×, a record mark ofpredetermined length can be recorded while adjusting Δ2=0, Δ1 to amaximum of 0.5*T, and Δ3 to from 0 T to 0.5 T. Up to a linear velocityof 2.4×, good recording characteristics are obtained. However, therecording linear velocity becomes higher and the linear velocity reaches4× (14 m/s), according to this method, it becomes more difficult toacquire sufficient overwrite characteristics.

[0068] In the case of the aforesaid phase-change optical recordingmedium, at a linear velocity of 4×, the more the erasing power isincreased, and the longer a rear cooling pulse FPm is lengthened, hencethe worse are the first overwrite characteristics. This means that theerasure rate of previous record marks is worse. This is because the marklength of the amorphous phase region of the record mark rear edgewidens, and the mark length increases. As the optimal range of erasingpower is narrow, the recrystallization rate is slower. In other words,the recording layer is sufficiently heated, and the velocity is reducedto grow the crystals at a lower temperature than the fastest speed atwhich crystals grow from the molten state.

[0069] For this purpose, in the present invention, at least at themaximum recording velocity, by completing the ending time of the rearpulse T−OPm earlier than the record mark ending part, overwritecharacteristics can be improved. In other words, it is effective to makethe rear cooling pulse width zero, or to shorten it as much as possible.

[0070] In the present invention, moreover, at least at one recordinglinear velocity, by starting a front pulse, i.e., a front pulse of thepeak power 0.5 T to 1.25 T later than a starting point of the firstreference clock relative to the mark, jitter can be suitably controlledat a low level.

[0071] It is also effective to apply these conditions to a range fromthe intermediate linear velocity to the maximum linear velocity amongrecordable linear velocities ranges to the phase-change opticalrecording medium. This means assigning a maximum width of T−OPm to“dTera” relative to the position b of FIG. 3.

[0072] Here, the intermediate recording linear velocity is 2.4× whichcorresponds to 3.49×2.4 m/s and the maximum recording linear velocity is4× which corresponds to 3.49×4 m/s in that case.

[0073] In FIG. 3, “dTop” is a variable range of a starting time of afront heating pulse relative to “a” (a: the position which is 1 Tdelayed from the starting point of the first reference clock relative tothe recording mark). If the front heating pulse starts earlier thanposition “a”, it is assigned (+) and if it starts later, it is assigned(−). Therefore, if it is 0.5 T to 1.25 T delayed from the starting pointof the first reference clock relative to the recording mark, “dTop” lieswithin a variable range of −0.25 to +0.5 T. “OP” is the irradiation timeof the peak power Pp (heating pulse). “OP1” is the irradiation time ofPp of the front pulse. “OPj (j=2−(m−1))” is the irradiation time of Ppof the intermediate pulse. “OPm” is the irradiation time of Pp of therear pulse. “FP” is the irradiation time of the bias power Pb (coolingpulse). “FP1” is the irradiation time of Pb of the front pulse. “FPj(j=2−(m−1))” is the irradiation time of Pb of the intermediate pulse.“FPm” is the irradiation time of Pb of the rear pulse. “dmp” is thevariable range of the starting time of the intermediate heating pulse.“dlp” is the variable range of the starting time of the rear heatingpulse. “dTera” is the variable range of the ending time of the rearcooling pulse relative to “b” of FIG. 3. If the rear cooling pulse endsearlier than position “b”, it is assigned (+) and if it ends later, itis assigned (−). “dint” is the time from the end position of the rearcooling pulse to the starting position of the compensation pulse. “dera”is the irradiation time of the second erasing power (Pe2). In theabove-mentioned FIG. 3, “Pe2” has is the same value as “Pe1”, and “dint”and “dera” are 0.

[0074] Subsequently, with Pe2>Pe1, Pe2 is a power for which, ifcontinuous irradiation is performed at the recording linear velocity,the reflectance does not decrease compared to its value prior toirradiation. A compensation pulse which sets a time dint for irradiatingthe erasing power Pe1 and a time dera for irradiating Pe2 from theending time of the rear cooling pulse to optimal times, is added. Thismultipulse pattern may comprise one or more compensation pulses ifnecessary.

[0075] This compensation pulse may be applied to recording of all recordmark lengths or to shorter record mark lengths. In this case, recordmark length is preferably 3 T, 4 T, and 5 T. All of these, 3 T alone, or3 T and 4 T are preferable (there is no case of 3 T, 5 T, or 5 T only).In particular, although the shortest record mark length is 3 T in DVD,it may be applied only when recording is performed to form record marklength of 3 T, 4 T or 5 T. These compensation pulses eliminate dataremaining after erasing in a course of overwriting. For this reason,they are required in order to promote recrystallization. In addition tothe present purpose, this compensation pulse becomes more effective asthe recording linear velocity increases. The higher is the recordinglinear velocity, the more time is required from when the erasing poweris irradiated to raise the temperature of the recording layer to thetemperature of the molten state.

[0076] However, if it is attempted to increase the erasing power Pe1, asthis power is irradiated continuously or at regular intervals until thenext mark is recorded, the recrystallization region widens, or due tothe higher linear velocity together with the quenching effect, theamorphous phase region widens. Hence, by providing the compensationpulse, control of the rear edge of the record mark is easier. Theoptimal times for dera and dint are 0.2 T<dera<3 T and 0<dint<1 Trespectively. As a result, the erasing rate after the first overwritingare improved, and jitter characteristics improve. The range of eachheating pulse width OPk (k=1, . . . m) is 0.2 T to 0.8 T. In the case ofDVD, when it is applied to from 1× to 4× and recording is made by CAVfrom 1× to 2.4×, the reference clock corresponding to each linearvelocity varies continuously, but an optimal recording is attained byadjusting each heating pulse width by the sum of a time proportional tothe reference clock T and a fixed time independent from the referenceclock.

[0077] Specifically, this is (1/a) T*i+b*j (a, b, i, j are integers[nanoseconds]).

[0078] For recording at 4×, a=16, and to increase control timeresolution, the pulse width is set to T*i (1/16), which is mainly usedin CLV. To control from 1.7× to 4× by CAV, a=16 and b=1, and (1/16)T*i+1*j is used.

[0079] The sum of the front heating pulse and the front of coolingpulse, the sum of the intermediate heating pulse and the intermediatecooling pulse, and the sum of the rear heating pulse and the rearcooling pulse are basically 1 T, but the sum of the front heating pulseand the heat of cooling pulse and the sum of the rear heating pulse andthe rear cooling pulse are not limited thereto.

[0080] By adjusting the aforesaid sums within a range from 0.3 T to 1.5T, a record mark of predetermined length can be recorded.

[0081] In CAV recording from 1× to 2.4×, the pulse width is adjusted byT*i(1/6)+2*j.

EXAMPLES

[0082] Hereafter, the method of the present invention will be describedreferring to specific examples.

Example 1

[0083] A phase-change optical recording medium was prepared as follows.

[0084] As a transparent substrate in which record marks are formed inthe groove thereon, a polycarbonate substrate having a groove pitch of0.74 μm, a groove width of 0.25 μm, a groove depth of 25 nm and athickness of 0.6 mm was used. Each layers was formed on the transparentsubstrate by the sputtering method. Address information was provided ina wobble of the groove having a frequency of 818 kHz, with 180 degreesreversed phase depending on the information.

[0085] The lower dielectric protective layer was formed with thicknessof 69 nm on the aforesaid substrate using a target of ZnS:SiO₂=80:20(mol %). Next, the phase-change recording layer which isGe:Ag:In:Sb:Te=3:0.8:3.5:72:20.7 was formed so that its thickness was 14nm. Next, the interface layer was formed so that its thickness was 2 nmusing a multiple oxide target of ZrO₂:TiO₂:Y₂O₃=49:45:6 (mol %). Next, aupper dielectric protective layer was formed to a thickness of 11 nmusing a target of ZnS:SiO₂=80:20 (mol %). A SiC layer of thickness 4 nmand Ag layer of thickness of 140 nm were formed thereupon. Next, toimprove environmental resistance, an ultraviolet curing resin (SD318,Dainippon Ink and Chemicals, Incorporated.) was applied and hardened soas to form an environmental protection layer having a thickness of 5 μm.Finally, the aforesaid transparent substrate was affixed to theenvironmental protection later via an ultraviolet curing resin layer(DVD 003 [acrylic], Nippon Kayaku Co., Ltd.) with a thickness of 40 μmto obtain a phase-change optical recording medium.

[0086] Even when this phase-change optical recording medium wassubjected to a test at 80° C., and 85% RH, or a heat cycle test between25° C. and 40° C. at 95% RH, defects did not occur. Next, the aforesaidrecording layer was crystallized using a large caliber LD of wavelength810 nm (beam diameter: track direction 1 nm×radial direction 75 μm) at alinear velocity of 9 m/s, power of 900 mW and head feed rate of 18μm/rotation.

[0087] When DC light of 12 mW was irradiated to the phase-change opticalrecording medium by the optical head equipping the LD with continuouslychanging the linear velocity, reflectance began to decrease from thevicinity of a linear velocity of 9.5 m/s. Recording and reproductionwere performed using a pickup head having a wavelength of 657 nm and anobject lens NA of 0.65, and recording was performed at a maximum linearvelocity of 14 m/s to give a recording density of 0.267 μm. The mode ofmodulating recording data was (8, 16) modulation. Recording wasperformed so that the recording power was a maximum of 19 mW, the biaspower was 0.5 mW and the erasing power was 30% of the recording power.The number of pulses of each mark length is (n−1) (n=3-14).

[0088] The conditions in the case of recording by CLV at a linearvelocity of 14 m/s (4×) and by CAV at a linear velocity of from 1× to2.4× are shown in Table 1. Herein, “dTop” is written as “dTtop”, “OP1”is written as “Ttop”, “OPj”, and “OPm” are written as “Tmp”. Also,“dmp”, “dlp”, “dint” and “dera” were all set to zero. These conditionsare based on the method of FIG. 3.

[0089] In addition, “dTtop” shown in the table 1 was measured based from“a” of FIG. 3. When the starting time of the front pulse is earlier than“a” it is assigned (+) and if it starts later, it is assigned (−).Looking at the starting position of record mark (the time T earlier thana), “a” corresponds “dTtop=1 T”. “−0.25 T” refers to the position 1.25 Tapart from the record mark starting position, and “0.5 T” refers to theposition 0.5 T apart from the recording marl starting position. Here,the record mark starting position corresponds to a starting point of thefirst reference clock. TABLE 1 Linear velocity   14 m/s  8.4 m/s   35m/s Reference clock: T 9.55 nsec. 15.67 nsec. 38.22 nsec. Parameters(nsec) dTtop −(2/16)*T  (2/6)*T Ttop  (5/16)*T + 2 (2/6)*T + 6 Tmp (6/16)*T + 2 (1/6)*T + 4 Tmp  (6/16)*T + 2 (1/6)*T + 4 dTera  (6/16)*T (1/6)*T

[0090] The “dTtop” dependency of jitter after one overwriting at alinear velocity of 14 m/s is shown in FIG. 4. The recording power is 17mW. By delaying the starting position, the jitter margin widens. In theprior art, “dTtop” of FIG. 4 was more than zero, and the jitter afterone overwrite exceeded 9%. Even the case of 9% or less was within therange of 0 to 0.25 T, the margin was narrow. For this reason, “dTtop”must be finely controlled to approximately {fraction (1/16)} of thereference clock.

[0091] From FIG. 5, it is seen that the earlier the ending time of thecooling pulse at the rear edge (+side) is finished, the better are thecharacteristics. The power margin of the jitter during recording at arecording linear velocity of 2.4× and 4× for recording under theconditions of Table 1 which reflects these conditions, is shown in FIGS.6 and 7. A 4× recording power margin is guaranteed, and for 2.4×, thereis a large margin under a recording power of 15 mW, so 4× recording ispossible and there is downward compatibility.

Example 2

[0092] Using the same phase-change optical recording medium as inExample 1, as shown in Table 2, in the case of 4× recording, the pulsewidth was adjusted by a time proportional to a reference clock, and“dTera” was taken as T-Tmp. In the case of CAV recording at anintermediate linear velocity which is corresponded to a range of 8.4 m/sto 3.5 m/s when the maximum linear velocity is 14 m/s and minimum linearvelocity is 3.5 m/s, as shown in Table 2, the pulse width was adjustedby a time proportional to the reference clock and a fixed time.

[0093] As a result, for a linear velocity of 14 m/s, recording wasperformed at a recording power of 17 mW and erasing power of 5.3 mW. For8.4 m/s and 3.5 m/s, recording was performed at a recording power of 15mW and erasing power of 7.5 mW. In all cases, the jitter was 9% or lessup to 1,000 times of overwriting. TABLE 2 Linear velocity   14 m/s  8.4m/s   35 m/s Reference clock: T 9.55 nsec. 15.67 nsec. 38.22 nsec.Parameters (nsec) dTtop −(2/16)*T  (2/6)*T Ttop  (9/16)*T (2/6)*T + 6Tmp  (9/16)*T (1/6)*T + 4 Tmp  (9/16)*T (1/6)*T + 4 dTera  (7/16)*T (1/6)*T

Example 3

[0094] The same phase-change optical recording medium as in Example 1was used, and the recording layer material wasGe:Ag:In:Sb:Te=2:0.5:3.5:72.5:21.5. The pulse width was adjusted by atime proportional to a recording linear velocity of 6 m/s exceeding 1/3of the maximum linear velocity of 14 m/s, and, a time which wasproportional to the reference clock of 14 m/s, and a fixed time, and CAVrecording was performed. At 6 m/s and 8.4 m/s, the recording power was15 mW, at 14 m/s the recording power was 18 mW, and the jitter was 9% inall cases. The recording conditions are shown in Table 3. TABLE 3 Linearvelocity   14 m/s    6 m/s Reference clock: T 9.55 nsec. 22.22 nsec.Parameters (nsec) DTtop −(2/16)*T 2/6 *T Ttop  (6/16)*T + 1.8 Tmp (6/16)*T + 1.8 Tmp  (6/16)*T + 1.8 DTera  (6/16)*T 0

Example 4

[0095] The same phase-change optical recording medium as in Example 1was used, and recording was performed at a recording linear velocity of14 m/s and recording power of 17 mW. The recording conditions are asshown in Table 4. Each pulse width was adjusted to a time which wasproportional to the reference clock. For record marks from 3 T to 14 T,the compensation pulse was applied only when recording the record markof 3 T. The erasing powers were Pe1=5.3 mW and Pe2=6.0 mW. Thecompensation pulse starting time was set to dint=0 T and thecompensation pulse irradiation time (pulse width) was set to dera=0.5 T.As a result, when there is 9% jitter on the first overwriting without acompensation pulse, the jitter was 8% with the compensation pulse. Whenthere is 8% jitter after 1,000 times of overwriting without thecompensation pulse, the jitter was 7.5% with the compensation pulseafter 1,000 times of overwriting. Therefore, there is a large effect inimproving the first overwriting where high density and high linearvelocity are a problem with a phase-change optical recording medium.TABLE 4 Linear velocity 14 m/s Reference clock: T 9.55 nsec. Parameters(nsec) DTtop −(2/16)*T  Ttop (9/16)*T Tmp (9/16)*T Tmp (9/16)*T DTera(9/16)*T Dera (8/16)*T 3T only 0 4T-14T Pe1 (mW) 5.3 Pe2 (mW) 6  

Example 5

[0096] The same phase-change optical recording medium as in Example 1was used, and the recording condition was also the same as in Example 1expect dTtop.

[0097] dTtop dependency of jitter relative to each recording linervelocity at the first overwriting is shown in FIG. 8.

[0098] For the recording linear velocity of 14 m/s, recording wasperformed at a recording power of 19 mW and an erasing power of 5.7 mW.For the recording linear velocity of 3.5 m/s, recording was performed ata recording power of 16 mW and an erasing power of 8 mW. Especially withthe recording linear velocity of 14 m/s, the jitter exceeded 9% in theconventional range of dTtop which was 0 T to 0.5 T (the starting time ofthe front pulse starts 0.5 T to 1.0 T later than the starting point ofthe first reference clock). When dTtop is more than 0.5 T (the startingtime of the front pulse starts less than 0.5 T later than the startingpoint of the first reference clock), the jitter exceeded 9% with allrecording linear velocities.

Example 6

[0099] The same phase-change optical recording medium and the recordingmethod as in Example 1 were used expect that the material of therecording layer was changed to Ge:Ga:Sb:Te=4:2:73:21. Recording wasperformed at a recording linear velocity of 14 m/s, a recording power 18mW, the erasing power 5.6 mW. As a result, the jitter remained 9% orless up to 1,000 times of overwriting.

Example 7

[0100] The same phase-change optical recording medium and the recordingmethod as in Example 1 were used expect that the material of therecording layer was changed to Ge:Sn:Sb:Te=4.0:4.5:71.0:20.5. Recordingwas performed at a recording linear velocity of 14 m/s, a recordingpower 18 mW, the erasing power 5.4 mW. As a result, the jitter remained9% or less up to 1,000 times of overwriting.

[0101] According to the aforesaid first aspect, a recording method canbe provided in which there is downward compatibility, recordingcharacteristics are maintained even if there is downward compatibility,and recording characteristics are excellent even at a high linearvelocity.

[0102] According to the aforesaid second aspect, a recording method isprovided which permits CAV recording within a predetermined range ofrecording linear velocity from the minimum recording linear velocityrange to the maximum recording linear velocity range in which recordingcan be performed on the phase-change optical recording medium.

[0103] According to the aforesaid third aspect, a recording method isprovided which permits the recording property margin to be widened.

[0104] According to the aforesaid fourth aspect, a recording method isprovided which has excellent overwrite characteristics at a highrecording linear velocity.

What is claimed is:
 1. A recording method for a phase-change opticalrecording medium, comprising the step of: irradiating an electromagneticwave to a phase-change optical recording medium containing phase-changelayer at least at a recording linear velocity according to a multipulsepattern so as to perform writing and rewriting by inducing a reversiblephase change between a non-crystalline phase and a crystalline phase andutilizing a variation in optical constant cased by the reversible phasechange, wherein the multipulse pattern contains pulses of a peak power(Pp), an erasing power (Pe) and a bias power (Pb), wherein a startingtime of a front pulse when forming a mark, that is a front pulse of thepeak power, starts 0.5 T to 1.25 T later than a starting point of thefirst reference clock relative to the mark at least at a recordinglinear velocity, where T is a reference clock of the multipulse pattern.2. A recording method for a phase-change optical recording mediumaccording to claim 1, wherein the starting time of the front pulsestarts 1 T to 1.25 T later than the starting point of the firstreference clock.
 3. A recording method for a phase-change opticalrecording medium according to claim 2, wherein writing and overwritingare performed at a plurality of recording linear velocities, and thestarting time of the front pulse starts 1 T to 1.25 T later than thestarting point of the first reference clock with at least at a maximumlinear velocity among the recording linear velocities.
 4. A recordingmethod for a phase-change optical recording medium according to claim 3,the starting time of the front pulse starts 1 T to 1.25 T later than thestarting point of the first reference clock at least at an intermediateto maximum linear velocity or faster among the recording linearvelocities.
 5. A recording method for a phase-change optical recordingmedium according to claim 3, wherein the starting time of the frontpulse is adjusted depending on a recording linear velocity.
 6. Arecording method for a phase-change optical recording medium accordingto claim 1, wherein an ending time of a rear pulse, that is one of arear pulse of the peak power and a rear pulse of the bias power, endsT−OPm earlier than an ending point of the last reference clock relativeto the mark with at least one recording linear velocity, where OPm is airradiating time of the peak power relative to the rear pulse thereof.7. A recording method for a phase-change optical recording mediumaccording to claim 6, wherein writing and overwriting are performed at aplurality of recording linear velocities, and the ending time of therear pulse ends T−OPm earlier than the ending point of the lastreference clock at least at a maximum linear velocity among therecording linear velocities.
 8. A recording method for a phase-changeoptical recording medium according to claim 7, wherein the ending timeof the rear pulse ends T−OPm earlier than the ending point of the lastreference clock at least at an intermediate or faster velocity among therecording linear velocities.
 9. A recording method for a phase-changeoptical recording medium according to claim 1, wherein writing andoverwriting are performed at a plurality of recording linear velocities,and an irradiating time (OP) of the peak power of a front pulse, anintermediate pulse and a rear pulse, is adjusted with a sum of a timebeing proportional to a reference clock relative to each recordinglinear velocity and a time being independent from the reference clock,at least at a minimum linear velocity among the recording linearvelocities.
 10. A recording method for a phase-change optical recordingmedium according to claim 6, wherein writing and overwriting areperformed at a plurality of recording linear velocities, and anirradiating time (OP) of the peak power of a front pulse, anintermediate pulse and a rear pulse, is adjusted with a sum of a timebeing proportional to a reference clock relative to each recordinglinear velocity and a time being independent from the reference clock,at least at a minimum linear velocity among the recording linearvelocities.
 11. A recording method for a phase-change optical recordingmedium according to claim 9, wherein the irradiating time (OP) of thepeak power of the front pulse, the intermediate pulse, and the rearpulse, is adjusted with the sum of the time being proportional to thereference clock relative to each recording linear velocity and the timebeing independent from the reference clock, at the minimum linearvelocity to an intermediate linear velocity among the recording linearvelocities.
 12. A recording method for a phase-change optical recordingmedium according to claim 9, wherein the irradiating time (OP) of thepeak power of the front pulse, the intermediate pulse, and the rearpulse, is adjusted with the sum of the time being proportional to thereference clock relative to each recording linear velocity and the timebeing independent from the reference clock, at any linear velocity amongthe recording linear velocities.
 13. A recording method for aphase-change optical recording medium according to claim 1, whereinwriting and overwriting are performed at a plurality of recording linearvelocities, and an irradiating time (OP) of the peak power of a frontpulse, an intermediate pulse and a rear pulse, is adjusted with a timebeing proportional to a reference clock relative to each recordinglinear velocity, at least at a minimum linear velocity among therecording linear velocities.
 14. A recording method for a phase-changeoptical recording medium according to claim 13, wherein the irradiatingtime (OP) of the peak power of a front pulse, an intermediate pulse anda rear pulse, is adjusted with the time being proportional to thereference clock relative to each recording linear velocity, at one-thirdof a maximum linear velocity to the maximum linear velocity among therecording linear velocities.
 15. A recording method for a phase-changeoptical recording medium according to claim 9, wherein the irradiatingtime (OP) of the peak power of any pulse, is adjusted with the sum ofthe time being proportional to a reference clock relative to eachrecording linear velocity and the time being independent from thereference clock at a maximum linear velocity among the recording linearvelocities, and the time being independent from the clock reference is0.5 nano seconds or more.
 16. A recording method for a phase-changeoptical recording medium according to claim 9, wherein the recordinglinear velocity continuously changes along a radius direction from aninner circumference to an outer circumference of the phase-changeoptical recording medium.
 17. A recording method for a phase-changeoptical recording medium according to claim 1, wherein the multipulsepattern, relative to at the shortest mark among record marks, furthercontains at least one compensation pulse including a pulse of theerasing power and a pulse of a second erasing power which is higher thanthe erasing power, after the rear cooling pulse, where recording isperformed with at least a recording linear velocity.
 18. A recordingmethod for a phase-change optical recording medium according to claim 6,wherein the multipulse pattern, relative to at the shortest mark amongrecord marks, further contains at least one compensation pulse includinga pulse of the erasing power and a pulse of a second erasing power whichis higher than the erasing power, after the rear cooling pulse, whererecording is performed with at least a recording linear velocity.
 19. Arecording method for a phase-change optical recording medium accordingto claim 17, wherein writing and overwriting are performed at aplurality of recording linear velocities that are one of continuous andinterval, the multipulse pattern contains at least one compensationpulse in the case that recording is performed at least at the maximumlinear velocity among the recording linear velocities.
 20. A recordingmethod for a phase-change optical recording medium according to claim 1,the peak power has two or more power levels which are selected accordingto each pulse.